Luminescent lamp



H. W. LEVERENZ LUMINESGENT LAMP June 29, 1943.

iled Feb. 28, 1941 2 Sheets-Sheet l INVENTOR. Hl/MB/.DT W LEVERENZ .A TTRNEYA June 29, 1943. H. w. LEvERENz LUMINESCENT LAMP Filed Feb. 28, 1941 2 Sheets-Sheet 2 `Patented June 29, 1943 gaaanz ENT OFFICE N LUMINESCENT LAMP Humboldt W. Leverenl, South Orange, N. J., assignor to Radio Corporation of America, a corporation of Delaware Application February 28, 1941, Serial No. 381,032

11 Claims.

My invention relates to improvements in luminescent lamps and particularly to lamps and lamp `auxiliaries which in'combination produce light of high intransic brilliance.

Luminescent lamps are known wherein a coating oi' finely divided phosphor or luminescent material is provided on Ythe interior surface of an envelope which material upon excitation by corpuscular or radiant energy becomes luminescent. The intrinsic brilliance of such devices is very low and they are not adapted for the production of light of high intrinsic brilliance. Further disadvantages cf such lamps resides in the fact that the luminescent material which is in. a ilnely divided powdered yform absorbs as well as diffuses an appreciable proportion of the emitted light.

In my copending application Serial No. 348,790, illed July 31, 1940, and now Patent No. 2,298,947 issued Oct. 13, 1942, I described a luminescent lamp of exceptionally high intrinsic brilliance wherein the luminescent material was composed of solid elongated phosphor bodies. I likewise described in my prior application a lamp utilizing the cumulative effect of a plurality of luminescent solids comprising transparentphosphor members to provide an extended excitation volurne in a transparent luminescent solid.

Objects of my present invention include providing `luminescent lamps of exceptionally. high intrinsic brilliance; lamps of high intrinsic brilliance having` a wide range of colors or band spectrum emissions within the ultra-violet and infra-red portions of the spectrum; lamps of exceptionally high intrinsic brilliance of Athe electron discharge type capable of utilizing the excitation energy more eillciently. Another object of my invention is to provide a lamp of the type described which may be modulated with respect to the intensity of the developed light of high intrinsic brilliance. A further object is to provide a highly eiliclent lamp of smaller. dimensions than heretofore practicable. Still further objects of my invention are to provide auxiliary means to control the paths of corpuscular excitation energy in a lamp excited by corpuscular radiation and lamps capable of propagating light with highly directional characteristics with high luminous efficiency and relatively low excitation potentials,

In accordance with my invention I provide a luminescent lamp excitable by corpuscular energy such as an electron discharge wherein the material which becomes excited under the incident energy comprises elongated transparent phosphor bodies in combination with means to subject the bodies to corpuscular radiation incident thereon over controlled paths intercepting the bodies at angles other than normal to the surface of the bodies. More particularly in accorda-nce with my invention I provide means for use with the devices of the type described to direct luminescence exciting electrons upon the elongated transparent phosphor bodies along paths intercepting the bodies at angles other than normal to the surface of the bodies. Still further means are provided for developing light of high intrinsic brilliance and for varying or modulating the intensity of the light developed. These and other objects, features and advantages of my invention will become apparent to those skilled in the art when considered in view of the following description and the accompanying drawings in which:

Figure 1 is a longitudinal cross sectional view and schematic circuit of one form of luminescent lamp and auxiliary apparatus made in accordance with my invention;

Figure 2 is a cross section of the device shown in Figure 1 taken along the lines 2-2; and

Figures 3 and 4 are views similar to Figures 1 and 2 showing a further modification of my invention.

The lamp shown in Figures 1 and 2 is particularly adapted for producing high intensity light beams such as for search-light use or other applications wherein a high concentration of light from` a source of high intrinsic brilliance is desired. The lamp shown is of the type described in my above-mentioned copending application the exciting energy being corpuscular excitations such as highvelocity electrons. The lamp of Figure 1 comprises an elongated evacuated envelope l closed at one end of the envelope by a lens portion 2. 'I'he envelope I with the exception of the lens portion 2 is preferably provided on its exterior surface with a light opaque reflecting coating 3 which prevents liberation of light over the length and at one end oi' the envelope, directing light through the portion 2 in the form of a beam oi' high illuminating value.

In accordance with my invention I provide a plurality of transparent solid phosphor bodies comprising thin plate-like phosphor sheets I0 which are preferably of rectangular shape su ported within theenvelope I and separated one from the other by predetermined distances depending upon the operating parameters hereinafter set forth. It will be noted that I have shown two pairs of three sheets I0 designated Illa, 10b and |0c. I provide intermediate the sheets Ia a plurality of cathodes II which may be of the directly or indirectly heated type coated on their exterior surfaces with barium and strontium oxides or other electron emitting material. While I have shown a plurality of cathodes I I, it will be obvious that a single cathode of rectangular shape may be used. Between the sheets Illa and the cathodes I I I provide electron permeable anodes I2a to direct the electrons from tlhe cathodes II and project them toward and upon the phosphor sheets IIJa.

In accordance with a further teaching of my invention the sheets IIla may be of insufficient thickness to absorb all the energy of the electrons impinging thereon. Thus the electrons deliver the greater portion of their energy to the phosphor sheets I0a but retain suflicient energy to pass through these sheets into the space on the opposite side from the cathodes II. The electrons passing through the sheets Illa are re-accelerated by the anodes I2b and impinge on the plates I0b which are likewise of insufllcient thickness to absorb all of the electron energy, whereupon the electrons are again accelerated by the anodes I2C and impinged on the phosphor sheets IIlc which are Preferably of sufficient thickness to absorb all the electron energy. The sheets IIJc may be of the same thickness as the sheets IIJa1 and I0b provided a lower potential is applied to the anodes I2c than to the anodes I 2a and I2b. While I have shown only three phosphor sheets and their associated anode structures on opposite sides of the cathodes II, lt will be obvious that the systems of phosphor sheets and anodes may be repeated to obtain even higher total brilliance. Additional cathodes or thermionic emitters may likewise be provided between the sheets Ia and IIIb and between Illb and I0c.

The ratio of maximum dimension, such as the length of the sheets I0, to the minimum dimension, such as their thickness, should preferably be no less than 5 to 1, although a ratio of 3 to 1 may be sumcient such as where a plurality of sheets placed end to end are used. With these and greater ratios of length to minimum dimension the length is suicient to exhibit total lnternal reflection of light predominantly along and within the length of the phosphor sheets. Likewise the sheets I0 preferably consist of a single crystal of the phosphor. By single crystal is meant a crystal of both perfect and imperfect symmetry, and therefore this term includes a twin crystal, especially twinning of the interpenetration type which produces a minimum of optical inhomogeneity.

The potentials applied to the anodes I2 may be of the order of 10,000 to 300,000 volts positive with respect to the cathode potential or may be of this order alternating potential depending upon the thickness of the phosphor sheets I0. However, the potentials applied to the various anodes may be different, with the associated phosphor sheet thickness being chosen lnsufcient to absorb all of the electron energy for the desired anode operating potential.

I have found in accordance with a further teaching of my invention that the eiiiciency of solid phosphor bodies may be increased by increasing the secondary electron emission occurring at the surface of or within the solid phcsphor bodies. Therefore, ln accordance with this teaching of my invention I provide means in combination with the structures I have described to direct the electrons such as from the cathodes II upon the phosphor sheets I0a and further upthe adjacent anode.

on the sheets IIlb and Ic at acute anglesthereby increasing the secondary electron emission of the phosphor sheets.

Referring again to Figures 1 and 2 I provide means to generate a magnetic field extending longitudinally over the length of the phosphor sheets, such as a longitudinal magnetic i'leld generating coil I5 which incldses substantially the entire length of the envelope I. The use of such a coil is obviously impractical and unnecessary in combination with conventional fluorescent lamps excited principally by ultra-violet light generated in a vapor discharge and wherein the generated light is propagated in substantially all directions over the length of the lamps. However, in a lamp made in `accordance with my invention the light propagation is through the end of the envelope I such as though the transparent portion 2 and the exciting energy is electron irradiation which may be controlled by my magnetic means. As indicatedabove, the spacings between the adjacent sheets I0, such as between the sheets Illa and IIlb and between I0b and I0c, are so chosen that the electrons liberated from the cathodes II and impinglng upon the plates Illa, or the electrons passing through the sheets Illa and IIlb follow curved paths incident upon the phosphor sheets Illa or succeeding sheets at an acute angle so that the impinging electrons liberate secondary electrons greatly in access of the number of impinging electrons. The impinged surfaces of the phosphor sheets thereby acquire high positive potentials due to the loss from the surfaces of secondary electrons and the surfaces are thus driven to a potential substantially equivalent to that; of On the other hand, if the secondary electron emission is less than unity, the surfaces of the sheets I0 acquire limiting potentials which decelerate the approaching electrons thereby reducing the efficiency of the device.

The distance D, through which an electron moves toward an electrode in a crossed magnetic and electrostatic field may be represented by the where E is the electrostatic potential gradient in electro-magnetic units per centimeter, `H is the magnetic field strength in gausses, e/m is the ratio of charge to mass of the electron and t is the time in seconds.

Equation 1 may be simplied assuming the spacing betweenthe cathode and phosphor body as equal to D and becomes:

which in practical units, where V is expressed in volts impressed between the cathode and phosphor body, becomes:

11.3V D2( H, i

Obviously for a spacing between the cathodes II and the sheets Illa equal to D in the above equation the electrons from the cathodes I I would not impinge on the sheets IUa. The actual separation between the cathodes and the adjacent plates should, therefore, be less than the value D given above in terms of the potential differences and the magnetic field.

The increase in ysecondary electron emission occasioned by the use of the magnetic neld resuits in a higher energy conversion eiilciency thereby developing more light for given enersy input levels. Thus, the probability of an electron impinging on a phosphor surface is increased, especially in devices utilizing phosphor bodies in the form of single crystal rodsy as disclosed in my above-mentioned application. As a result, the size of thel device may be decreased while still retaining the advantages of high levels of illumination and even greater eiilciencies than devices used heretofore.

The light output of the device shown in Figures 1 and 2, may be controlled or modulated by the use of a grid structure (not shown) surrounding the cathodes, by varying the electrostatic field intensity or by varying the magnetic field intensity. Thus, modulation may be effected by varying the quantity oi' electrons flowing to the phosphor bodies. Similarly an increase in the ptential applied between the cathodes andthe anodes i2a will increase the number of electrons ilowing through the phosphor sheets Ita and consequently increase the light output from the sheets ib and I 0c. However, such increasel in potential will cause the angle of incidence which the electrons make with the plane of the sheets IIJa to be somewhat greater, thereby reducing the efllciency of secondary electron liberation from the impinged phosphor sheet and resulting in a decrease in the total light output. Similarly u an increase in the strength of the magnetic field for a given spacing between the cathode and sheets ina will produce increased secondary electron emission from the impinged phosphor sheets but when the magnetic field is increased to such a value that the value of D in the above equations is less than the distance separating the cathode and sheets Illa, the electrons will fail to impinge on the phosphor sheets reducing the light output to a very low value or zero value. Electrons liberated by the cathodes il are liberated with a finite emission velocity which is added to the velocity produced by the potentials applied to the anodes, as a consequence the electrons irnpinging on the surface of the phosphor sheets with a relatively narrow'range of velocity and for any given magnetic field will follow paths of different curvatures to the phosphor sheet. Con,- sequently small variations in the strength of the magnetic field from the ileld strength at which the electrons are just grazing the phosphor sheet surface will produce large variations in light output of the device. In this manner the light output may be varied over'very wide limits with relatively small variations in the magnetic field strength. For purposes of control I have shown a magnetic coil. i as energized from a source of direct current potential i6. Modulating potentials may be applied in series with the potential source iB which for modulating purposes is adjusted to a point at which the electrons from cathodes Il are just grazing the surface of the phosphor sheets Illa, the modulating potential then being applied such as at i1 to control the light output of the device.

While I have described my invention with respect to a modification wherein the transparent phosphor bodies are in the form of sheets, my invention is susceptible of use wherein the bodies are of cylindrical form. Referring to Figures 3 and 4 the envelope I including the lens or transparent portion 2, reilecting portion 3, and coil Il are similar to those shown in Figures 1 and 2. The phosphor bodies, however, are in theform of cylindrical phosphor members two of which are 'shown at 20a. and 20h. In this modification a single cathode 2| may be provided coaxially of the members 20a and 20h with the anodes in the form of wire mesh screen. so as to be electron permeable, being interposed between the cathode 2| and member 20a as shown at 22a and between the member 20a and 20h, as shown at 22h. The cylindrical assembly comprising the. cathode phosphor members and anodes may be supported by transparent cross shaped members 23 located at the opposite ends of the envelope. Obviously additional support members may be utilized between the ends of the structure -if such are desired or necessary because of thelength thereof.

The spacing between'the cathode and the member 20a and between 20a and 20h may be chosen in the same manner as described with reference to Figures 1 and 2. Likewise the potentials applied between the cathode and anodes are chosen *to provide penetration of the electrons through the phosphor member 20a. Similarly additional cylinders of solid transparent phosphor material may be utilized asvdescribed in connection with Figures 1 and 2.

For the cylindrical phosphor body construction the above equations are modified in terms of the radius R, measured in centimeters, of the cylindrical phosphor body. From the above equations:

#Gay

which becomes While I have indicated the preferred embodiments of my invention of which I am now aware aid have also indicated only several specific applications for which my invention may be employed, it will be apparent that my invention lis by no means limited to the exact forms illustrated or the use indicated, but that many variations may be made in the particular structure used and the purpose for which it is employed without departing from the scope of my invention as set forth in the appended claims.

I claim:

1. A luminescent device comprising an elongated envelope having a transparent end portion, a substantially optically transparent luminescent phosphor body extending longitudinally of said envelope, means oppositely disposed from and exposed to said body to develop a flow of electrons radially of said envelope, means to direct said electrons in a direction substantially normal to the surface of said body, and means to direct said electron flow along paths intersecting the longitudinal surface of said body at oblique angles to excite said body to luminescence and liberate secondary electrons from the surface of said body.

2. A luminescent device comprising an elongated envelope having a transparent end portion, a light reilective coating on the walls of said envelope with the exception of said end portion, a plurality of substantially optically transparent luminescent phosphor bodies extending longitudinally of said envelope, means to develop a flowv of electrons radially of said envelope and in a direction substantially normal to the surface of said bodies and means to direct said electron flow from said direction and along curved paths incidentupon said bodies at oblique angles with respect to the longitudinal surfaces of said bodies gated envelope, means to develop a magnetic field having lines of force extending longitudinally of said envelope, a plurality of elongated phosphor bodies within said envelope, immersed in said field and positioned with their longitudinal surfaces substantially parallel to said field, :and means to develop a ow of electrons moving transversely of said field and intercepting said bodies at oblique angles with respect to the surfaces thereof to liberate secondary electrons from said surfaces and to excite said bodies to luminescence.

4. A luminescent device comprising an envelope, a plurality of elongated optically transparent phosphor bodies within said envelope, said bodies being of suflicient length to exhibit total internal reflection along the length thereof, means to subject said bodies to an electron iiow to develop light, means to intensify the light developed by said bodies comprising a magnetic field genera-ting coil extending longitudinally of said bodies to direct said electron flow upon said bodies at oblique angles with respect to the surfaces of said bodies, and means associated with said magnetic field generating coil to vary the intensity of said light whereby said light may be modulated.

5. A luminescent device comprising an evacuated envelope, a source of electrons, a luminescent optically transparent phosphor body exposed to said source, an anode between said source and said phosphor body to direct electrons thereto, and magnetic field generating means surrounding said envelope and developing magnetic lines of force substantially parallel with the surface of said phosphor body to direct said electrons along curved paths intersecting said phosphor body at oblique angles with respect to the said exposed surface to develop light and liberate secondary electrons from saidphosphor body.

6. A luminescent device comprising a source of electrons, a. plurality of solid optically transparent phosphor bodies, at least one of said bodies ing bodies being at increasing distances from said one body and said source, and means comprising a. plurality of anodes to direct electrons from said source through said bodies and upon the body most remote from said source thereby developing luminescence in each of said phosphor bodies.

7. A device as claimed in claim 6 including means to develop a magnetic field having lines of force extending substantially parallel with the.

surface of the transparent phosphor body exposed to said source to direct electrons along curved paths intercepting said bodies.

being directly exposed to said source the remain l 8. A luminescent device comprising an electron source to liberate electrons, a plurality of optically transparent phosphor bodies each of said bodies being spaced at progressively increasing distances from said source, said bodies having their minimum dimension in the direction of spacing from said source, an anode between the said source. and the nearest adjacent phosphor body and an anode between each of the remaining phosphor bodies to accelerate electrons from said source, through said adjacent phosphor body and upon the body most remote from said source.

9. A luminescent device comprising a source of electrons, an electron permeable optically transparent phosphor body on opposite sides of said source an additional phosphor body positioned to receive electrons from said source passing through said first-mentioned 'phosphor body on opposite sides of said source, and an anode between said source and an anode between said bodies to direct electrons from said source through said first-mentioned phosphor body and upon said additional phosphor body.

l0. A luminescent device comprising an electron source, a cylindrical transparent electron permeable phosphor body surrounding and coaxial with said source, means to direct electrons from said source through said body, .phosphor means positioned to intercept electrons passing through said body and an anode between said body and said phosphor means to reaccelerate electrons passing through said body.

11. A device as claimed in claim l0 including a magnetic coil coaxial with said cylindrical phosphor body to direct the electrons from said source along curved paths intersecting said body and said phosphor means to liberate secondary electrons therefrom in excess of the number of electrons from said source impinging thereon.

HU'MBOLDT W. LEVERENZ. 

